. Oncogenic transformation of cells occurs via the mutation of genes whose protein products function in the metabolic pathways that control cellular growth and division. Stimulation of cells to divide, either by the addition of mitogens, or bytheexpression of oncogenes is accompanied by the alterations in the intracellular levels of a number of metabolites. One of these is the compound diacylglycerol (DAG). Diacylglycerol is produced via the hydrolysis of cellular phospholipids by the action of two types of enzymes. The action of phospholipase C's (PL-C) upon phospholipids produces DAG and "phosphoheadgroup", whereas the action of phospholipase D's (PL-D) produces phosphatidic acid (PA) and "headgroup". The PA thus produced can be further hydrolyzed by PA phosphohydrolase yielding DAG and inorganic phosphate. This application proposes an investigation of DAG and PA metabolism in cells transformed by middle T, the oncogene of polyomavirus. Specifically, there are three goals: (1) to determine the steady-state levels of DAG and PA in transformed and control cells, (2) to investigate the enzymatic basis (vis-a-vis PL-Cand PL-D) of DAG production in these cells, and (3) to determine the phospholipid sources(s) of DAG and PA. These experiments will provide a better understanding of the mechanisms by whichDAGproduction is regulated and how this regulation is perturbed by the expression of an oncogene. This information may, in the long term, lead to the identification of potential therapeutic targets whose manipulation would be ofvalue in the chemotherapy of cancers.